#include <stdio.h>
#include "math.h"

int main()
{
    double e = 0.1,b = 0.5,c,d;
    long int i;
    for(i = 6;;i*=2)
    {
        d = 1.0 - sqrt(1.0 - b*b);
        b = 0.5 * sqrt(b*b + d*d);
        if(2*i*b - i*e < 1e-15)
        break;
        e = b;
    }
    printf("pai = %.15lf\n",2*i*b);
    printf("The number of edges of required polygon:%ld\n",i);
}